Transformer



March 15, 1949. s, BEAMER 2,464,287

TRANSFORMER Filed Sept. 30, 1946 'huw INI mit.,

ATTORNEY Patented Mar. 15, 1949 UNITED STATES PATENT OFFICE TRANSFORMER Scott Beamer, Oakland, Calif. Application September 30, 1946, Serial No. 700,288

9 Claims.

The present invention relates to transformers, and particularly to a transformer for dimming neon tubes or the like.

As the use of neon lighting is becoming more widespread, and as neon tubes are being used more and more for illuminating as well as advertising and decorating purposes, the need for a practical method of varying the intensity, or what is commonly referred to as dimming of the neon light is becoming acute.

It is the object of the present invention to provide a neon dimming transformer or a transformer in which the current output may be varied to vary the intensity or brilliance of the neon tube, and at the same time, to maintain a constant ignition voltage. The manner in which this object is attained, and further and more specific objects and advantages of the invention are made apparent in the following specification wherein reference is made to the accompanying drawings.

In the drawings- Fig. 1 is a diagrammatic View of a typical neon transformer embodying the present invention;

Fig. 2 is a similar view illustrating the direction of current flow and flux;

Fig. 3 a cross-section of the transformer core taken along line 3-3 of Fig. 1; and

Fig. 4 an enlarged fragmentary detail view disclosing a specific joint construction on an exaggerated scale.

The term neon as used herein is not to be taken as restricting the invention to the application of lights involving the use of neon gas, but is used in its broader sense and should be taken as including any arc stream or electrical discharge in a gas, gas-filled tube, vacuum or partial vacuum.

Referring to the drawing in detail, the core I of my transformer comprises two end sections 2 and 3 and three leg sections 4-5-6 connecting the same, the leg sections being spaced to provide two windows 'I and 8. The entire core is made up of laminations in a conventional manner, the laminations of the three legs being formed integral with those of the end section 3 in E shape, while the laminations of the end sections 2 are I-shaped and are joined to those of the legs as at 9.

While, of course, the design of the core may vary to suit requirements, I might state that in a satisfactory transformer constructed by me, the uniform height of the stack of laminations is 1.75 inches, the width of the end sections .788 inch,

the width of the outer legs 4 and 6 the same, that i is .788 inch, and the width of the central leg 1.29.

A primary coil I is mounted upon the central leg adjacent to the end piece 2 and is connected to a source of alternating current, preferably of apressure of 110 volts. A secondary coil Il is mounted upon the central leg adjacent to the end low impedance so as to reduce the A. C. output current of the secondary to a minimum, say approximately 2 milliamperes when the shunts are uncontrolled. For this purpose I provide a novel arrangement of dimensioning-and mounting the shunts to provide a broad path for the magnetic leakage flux and to provide air gaps of minute proportions, barely perceptible to the eye, but still sufficient to divert a desired amount of iiux to the secondary.

My shunts are made of much larger cross-section than in the conventional method. They are made of thin laminations, preferably about to the inch, and the laminations run transverse to the lamnations of the core as shown. The length of the shunts corresponds to the thickness of the core, that is i375 inches in the instance selected; the height of each shunt is substantially the same as the width of each window and the width of each shunt is preferably somewhat in excess of the width of each outer leg, and somewhat less than that of the inner leg, in the present instance about 1.08 inches. Thus the cross-section of each shunt is greater than that of each outer leg, but less than the central leg.

The shunts are made to snugly but separably iit between the legs of the core in what may be referred to as driving fit. However, the laminations of each shunt are of slightly varying width, which may be due to imperfection in manufacture or to intentional design, so that some of the laminations will be in actual contact with thev legs. while others, and probably the large majority of them, will fall short of contacting the legs so as to leave minute air gaps I3, barely perceptible to the eye but plainly visible when held against a light. This is illustrated, in an exaggerated manner, in Fig. 4, the irregularities in the contact surfaces being such as to leave average air gaps of approximately 2/1oon of an inch.

The flux leakage of the shunts is controlled by two coils I4 mounted upon the shunts, the windings of the coils running in opposite directions on the two shunts, and the coils being connected in series with an impedance I5, which may be in the form of a conventional rheostat of a minimum resistance of 15 ohms.v When the circuit is open, that is, when the resistance is at a maximum, the flux leakage will be at a maximum and the output current of the secondary will, under the conditions outlined, be reduced to approximately 2 milliamperes. When the rheostat is cut into the circuit, and the resistance is reduced, a counter-ux will be set up in the shunts, increasing the output of the secondary by degrees to a contemplated maximum of approximately 60 milliamperes, depending upon the rheostat adjustment.

The operation of the dimming transformer is as follows: Leakage flux from the primary winding I0 is bridging the windows '5 8 of the transformer through the medium of the shunts I2. The reluctance, or resistance to flux, through the shunts determines the reactance of the transformer and the limiting or effective tube current. The leakage fluxes in theshunts I2 induce a current in the circuit which includes the windings I3 surrounding the shunts, and this current, assuming the said circuit to be closed, sets up a counter flux in the shunts opposing the leakage fluxes. Since the value of the current flowing in this shunt circuit, and thus the value of the opposing flux, may be varied through the impedance I4, the value of the leakage flux opposed thereby is correspondingly yaried and consequently the reactance of the secondary winding of the transformer is effectivelyfcontrolled by the impedance.

To insure a clear understanding of the princi ples of the present invention which result in the above defined operation, the accepted theory of operation of a conventional neon transformer may be outlined as follows: When the primary winding of the transformer is connected with a vsupply voltage, thisvoltage being symbolized by the character E-I in Fig. 2 of the drawings, and the secondary terminals are left open, a current Im passes through the primary winding I0. This current sets up a magnetomotive force in the core which results in the alternating flux Fm, and this flux Fm alternating in the core and threading both the primary and secondary winding sets up a back voltage in each of these windings, the voltage in the primary and secondary windings being in direct proportion respectively to the number of turns in the windings. The voltage so set up in the secondary winding by the flux Fm is symbolized by E-Z, and the back voltage so set up in the primary Winding is E-I which is in direct opposition to E-I and almost equal to it. Since E'-I is almost equal in opposition to E-I, the magnetizing current Im will be small because the resultant effective primary coilvoltage is small,

the-secondary of the transformer, the secondary voltage E-Z will cause a current 1 2 to ow through the impedance Z and through the secondary winding. This current I'-2 in flowing through the secondary winding willA set up a secondary magnetomotive force in thejcore, creating another alternating Ilux F-2 in opposition to the flux Fm. This new ilux F-2 will-create a voltage i'n the primary winding which will oppose and therefore effectively decrease the voltage E'-I and consequently permit anincreased flow of the primary current I-I. This increase in current I-I will set up a magnetomotive force which will create another alternating flux F-I opposite and substantially equal to the flux F-Z, and the resulting flux in the core will be practically the same as when the secondary circuit was open. Thus it would appear that as the current in the coils of the transformer increases, the opposing magnetomotive forces increase, but the resulting quantity of flux Fm remains practically 4 the same from no load to full load. However, this is not, strictly speaking, correct, because the increase in ampere turns (primary and secondary current) causes increased magnetomotive forces in the core, and a small part of the opposing uxes F-I and F2 leak or find their way across the windows I3, or in the case of a neon transformer, through the shunts I6 provided for this purpose. The flux that takes this path is called leakage flux and links only with the windings or coil from which it originates. Consequently, whenever there is a leakage flux, a back voltage or reactance is set up in the winding that causes the setting up of the flux. This back voltage in practice is referred to as leakage reactance. In a transformer, this leakage reactance causes the 'secondary terminal voltage to be lower at full load than at no load.

Now the impedance Z may be considered as being a neon tube having, for example, a length of forty feet operating on a voltage of 15,000 volts. Assuming a conventional alternating current supply, as the voltage at the beginning of the cycle rises there is no effect upon the tube until it reaches a value of about 15,000 Volts, which is equal to the ionization potential. At this instant the tube is ignited and starts to glow. At the same instant the resistance of the tube drops to a low value, and in order to limit the current in the tube to a reasonable value, there must be sufcient reactance in the transformer to limit the current output. The reactance of the conventional neon transformer is such that the voltage across the tube will drop to approximately '70% of the voltage at the time of ignition for the remainder of the half-cycle. The action as above described is of course repeated in every halfcycle.

In the conventional neon transformer, the shunts are provided to accommodate the leakage iiux, and the operation of the transformer when used with the neon tube is somewhat as follows: Starting at the beginning of the ux cycle, the impressed voltage E-I and the output Voltage E-2 simultaneously rise to almost the crest of the voltage wave before any current flow takes place. At an instant before the peak voltage is reached, the neon tube ignites. Effectively at that instant the load, impedance Z, is thrown across the secondary of the neon transformer. T-he current quickly rises in the secondary coil, building up the magnetomotive forces behind F-I and F-2, and since these fluxes are backed -by opposing magnetomotive forces equal in magnitude, they force the leakage fluxes FL-I and Flr-2 through the paths `provided by the shunts. Since these leakage iluxes in taking these paths thread only the coil from which they were generated, they create a high back voltage in both the primary and secondary coils and thus cause the secondary voltage to drop the instant the current starts to how -through the neon tube. The cire-ctive back voltage created by providing magnetic paths for the leakage flux limits the load current as would a high impedance added in series with any load. The shunts in a conventional neon transformer are usually built to limit the current in the tube to 30 or 60 Inilliamperes. It may be seen that if the air gaps I3 between the shunts and the core were widened, this would add irnpedance to the leakage flux, causing a decrease in leakage flux, a decrease in eiective secondary reactance, and -consequently an increase in the effective tube current. Thus itis apparent that the reluctance or resistance to flux of the shunts I2 is a measure of the reactance of the transformer, and is the determining factor in the effective tube current. This reluctance of the shunt path is ordinarily determined by the crosssectional area of the shunts, their length, and the length c-f the air gaps at their ends. In the present invention, howeve-r, the reluctance to leakage flux in the shunts is controlled by setting up an opposing flux in the shunts.

In the transformer of the present invention, the operation is similar to that described above. However, when the leakage fluxes FL-I and FL-Z begin to build up in the shunts, they set up a v-oltage in the shunt windings I4. If now the value of the variable impedance I5 is very high (circuit open), the voltage generated in the shunt coils has no effect because no current flows in the shunt coil circuit. Since the shunts are of unusually large cross-sectional area, and have unusually small air gaps, they offer very little reluctance to the fluxes FIr-I and FL2. These fluxes therefore have their maximum value, and the effective secondary coil reactances are a maximum and the limiting tube current is a minimum. On the other hand, if the value of the variable impedance I5 is low (say only 30 or 40 ohms), a current of correspondingly high value iiows in the circuit of the shunt windings I4, and this current sets up a counter flux FS in the shunts which opposes the leakage fluxes FL-I and Flr-2. age fluxes, the values of the leakage iiuxes are diminished in value corresponding to the value of the opposing flux, and the decrease in the value of the leakage fluxes results in a decreased effective reactance of the secondary coil of the transformer. Consequently, a much higher current is able to flow in the secondary coil and through the neon tube. As the impedance is in the form of a rheostat, the flow of current through the shunt windings may be Varied at will to increase or decrease the value of the fiux FS, and thus any desired output current up to the capacity of the transformer may be effected.

I have found that a transformer built in accordance with my invention as described above will satisfactorily dim a neon tube of 80% of the full load of the transformer from 100% luminous output to 5% or less. Furthermore, the dimming may be effectively accomplished with any of the commonly used gas-filled tubes even in view of Since the flux FS opposes the leakthe specific ignition characteristics of the different gases.

While I have described a particular type of transformer for the purpose of illustrating the invention, it should be understood that the princfples of operation set forth are applicable to other fundamental transformer forms. That is to say, the transformer need not necessarily be of the shell type but may be of the core type or any known form in which there is .provided a shunt or path for leakage ux.

I claim:

1. In a transformer of the character described, a core comprising two end sections andthree legs connecting the same, primary and secondary coils mounted upon the central leg in spaced relation and shunts snugly but separably fitted between the central leg andthe cute-r legs intermediate the coils, the shunts having irregular contact surfaces to provide locally confined air gaps between the shunts and the legs.

2. 1n a transformer of the character described, a core comprising two end sections and ,three legs connecting the same, primary and secondary coils mounted upon the central leg in spaced re lation and laminated shunts fitted between the upon the legs while others stop short of the legs 4to provide locally confined air gaps between the shunts and the legs.

3. In a transformer of the character described, a core havingr a pair of spaced legs, and a shunt snugly but separably fitted between the legs, the shunt having slightly irregular contact faces to provide locally confined air gaps between the shunt and the legs.

4. In a transformer of the character described, a core comprising two end sections and three legs connecting the same, primary and secondary coils mounted upon the central leg in spaced relation, and shunts fitted between the central leg and the outer legs intermediate the coils, the shunts having a'relatlvely large cross-sectional area and being shaped to form locally confined air gaps with the legs to provide a low impedance magnetic path adapted to reduce the output of a 15,000 volt unit to substantially 2 milliamperes.

5. In a transformer of the characterdescribed. a core having a pair of spaced legs, and a shunt snugly but separably fitted between the legs, the shunt consisting of laminations arranged with their ends facing the legs, and the laminations having minute variations in length whereby some of the laminations are made to contact the legs while others are spaced therefrom to provide slight air gaps.

6. In a transformer of the character described, a core having a pair of spaced legs, and a shunt snugly but separably fitted between the legs, the shunt consisting of laminations arranged with their ends facing the legs, and the laminations having minute variations in length whereby some of the laminations are made to Contact the legsL while others are spaced therefrom to provide slight air gaps, averaging approximately twothousands of. an inch.

'7. In a transformer of the character described. a core having a pair of spaced legs, and a shunt snugly fitted between the legs, the shunt having irregular contact faces to provide locally confined air gaps between the shunt and the legs.

8. In a transformer of the character described, a core having a pair of spaced legs, and a shunt snugly fitted between the legs, the shunt consisting of laminations arranged with their ends facing the legs, and some of the laminations stopping short of the other laminations to provide air gaps between the shunt and the legs.

9. In a transformer of the character described, a core having a pair of `spaced legs,. and a shunt snugly fitted between the legs, the shunt consisting of laminations arranged with their ends facing the legs, and some of the laminations stopping short of the other laminations to provide air gaps between the shunt and the legs, averaging approximately two-thousands of an inch.

SCOTT BEAMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,376,978 Stoekle May 3, 1921 1,943,464 Von Ohlsen et al. Jan. 16, 1934 2,265,700 Outt 1 Dec. 9, 1941 2,382,638 Keiser Aug. 14. 1945 

